The state of the art comprises a number of easily openable covers or closures, including covers where the outer layer is a protective, relatively thick plastic layer and the inner layer a metal layer or a corresponding gas and vapour tight layer, for instance an aluminum foil or a layer of high barrier plastics. Said known structures also comprise a multitude of grip devices and different sorts of tearing denotations.
In the case where the outer layer consists of plastic, however, easily openable structures generally have the drawback that the manufacturing procedure is a two step procedure, for instance a two step injection moulding operation. This necessitates some sort of later mounting or a complex mould arrangement.
The opening procedure of known covers may include a simultaneous penetration of the outer and inner layers, but the manufacturing procedure and the known structural measures often involve a very difficult balancing act, which unfortunately may result in an end product, which does not meet the high demands for reliable opening. In other cases the opening of the closure is a two step procedure, where the protective outer layer is opened first and the inner layer, generally called the membrane, thereafter is punctured.
According to the invention it has been realized that for obtaining the desirable objects, the following requisites are necessary:
the opening arrangement shall define a well defined tearing direction, the outer and inner layers shall be opened together but sequentially such that the outer layer is first broken through, after which the inner layer is penetrated, and additionally the outer layer, or the mechanically reinforcing layer, shall be manufactured in one single step, for instance by injection moulding.